Self-aligning roller bearing

ABSTRACT

A self-aligning roller bearing includes an external ring with one curved external track, an internal ring with two curved internal tracks, two rows of rollers disposed between the external and internal rings, and a guide ring. The guide ring is located between the rows of rollers and is preferably configured as an circular annular disk. The guide ring has a rectangular cross section with the center line of the cross section running parallel to the bearing axis. The guide ring may also be dimensioned in such a way that the rollers are axially prestressed. The front faces of the rollers which face the guide ring are configured in a manner that the front faces only touch the guide ring at one point.

BACKGROUND OF THE INVENTION

1. Field of the invention

The invention relates to a self-aligning roller bearing with two rows ofsymmetrical rollers, an outer ring with a curved outer track, an innerring with two curved inner tracks, and a guide ring which is providedbetween the rollers and which is made as a circular ring disk

2. Description of the Related Art

Antifriction bearings which are used to transfer radial and/or axialloads to rotating parts are divided according to the shape of theirroller bodies into ball bearings on the one hand, and roller bearings onthe other. In roller bearings, it is distinguished between cylinder,barrel-shaped, needle, tapered and self-aligning roller bearings.Self-aligning roller bearings contain two rows of barrel-shaped rollerswith roller axes which are tilted relative to the bearing axis. Theouter track is hollow-spherical so that in case of alignment faults andwhen the assigned shaft sags, the rollers can be adjusted in anoscillating manner in the outer track. The profile of the tracks isgenerally rather narrowly matched to the profile of the rollers. Thedifferent embodiments of the self-aligning roller bearings differ bothin size itself and also in the size and shape of the rollers. Thus,there are both embodiments with symmetrical rollers and also those withasymmetrical rollers. In addition, there are embodiments with andwithout rims.

Self-aligning roller bearings have been used for more than fifty years.Due to their high bearing capacity, they have proven effective and areused wherever high impact-like forces must be accommodated and alignmentfaults and greater sagging of the assigned shaft must be expected. Themain applications are heavy rollers and supporting rolls, marine shaftsand rudder posts, rock crushers, crankshafts, transmissions, vibratingscreens, milk, grinding and crushing machines. Due to the numerousapplications, during decades of use of self-aligning roller bearings,attempts have been made again and again to further increase bearingcapacity and reduce production costs by structural modifications. Thus,there have been attempts to guide the rollers with a loose guide ringinstead of a middle rim permanently connected to the inner ring, or toabandon special guides completely so that the roller are guided solelyby a cage. Normally, one such cage is designed to keep the individualrollers of a row of rollers at a uniform distance to one another andthus, to prevent their mutual contact. In a self-aligning roller bearinghowever, the rollers of the two rows of rollers move under load onto oneanother so that wear of the cage occurs when the guidance of the rollersis not assumed additionally by a middle rim or a guide ring.

Whenever a fixed middle rim or a loose guide ring is used in aself-aligning roller bearing, in the prior art, this middle rim or thisguide ring has a trapezoidal cross section. Thus, German patent 644 181,FIGS. 2 and 3, published in 1937, discloses a self-aligning rollerbearing in which a loose guide ring is used to guide the rollers. Here,the width of the trapezoidal guide ring is so large that The rollers arepressed to the sides of the self-aligning roller bearing. U.S. Pat. No.2,740,675 published in 1956 discloses a self-aligning roller bearing inwhich there is a loose trapezoidal guide ring located on the inner ringbetween the rollers of the two rows of rollers. To obtain optimumfriction behavior under different radial loads, the width of the guidering should correspond exactly to the distance between the rollers ofthe two rows of rollers. Both in the self-aligning roller bearing aspatented in German patent 644 181 and also in the self-aligning rollerbearing patented in U.S. Pat. No. 2,740,675, the guide ring is designedon the one hand to safeguard the distance between rollers of the tworows of rollers and on the other to prevent crossing of the rollers.U.S. Pat. No. 5,586,826 which just recently issued discloses aself-aligning roller bearing with a trapezoidal guide ring. Here, thefriction will be reduced by a special configuration of the rollers.

SUMMARY OF THE INVENTION

The primary object of the invention is now to make available aself-aligning roller bearing with high bearing capacity which on the onehand, can be easily and economically produced, on the other, has lowfriction even under high load so that high rpms are possible and a longservice life is ensured

The self-aligning roller bearing in accordance with the presentinvention in which the aforementioned object is achieved includes aguide ring that has a rectangular cross section and the cross sectionalcenter line of the guide ring that runs parallel to the bearing axis.The advantage of a guide ring with a rectangular cross section comparedto a guide ring which is made trapezoidal consists first of all in thatthis guide ring can be produced especially easily and consequentlyfavorably. But mainly, the attained advantage is that a uniform distancebetween the rollers of the two rows of rollers is always ensured.

In conjunction with the above described measures one advantageousembodiment of the self-aligning roller bearing in accordance with thepresent invention acquires special importance; the guide ring isdimensioned such that the rollers are axially prestressed. Therefore,the guide ring exerts a force on the rollers at an acute angle to theroller axes, by which displacement of the contact points between therollers and the outer track and the inner tracks is caused. Therefore,the pressure ellipses between the inner tracks and the rollers areshifted to the end face of the self-aligning roller bearing. Withoutthis prestress, the rollers touch the outer track and the inner tracksat the location of their largest diameter so that the lines of forceaction of the inner ring and inner track - rollers and rollers - outerring and outer track, cause crossing of the rollers. By displacement ofthe points of contact which is caused by the indicated prestress, thelines of force action of the inner ring and inner track - rollers androllers - outer ring and outer track, are at an angle which reduces thecrossing of the rollers.

In the self-aligning roller bearing in accordance with the presentinvention the guide ring, as is known, is preferably made as a looseguide ring. The guide ring is therefore guided on the inner ring, but isnot joined to it. In this way, if necessary, a different material can beeasily used for the guide ring than for the inner ring. But mainly, aloose guide ring has the advantage that the peripheral component of theguide ring speed is balanced by the co-rotation of the guide ring, i.e.approaches zero.

It is especially advantageous if in the self-aligning roller bearing,the end faces of the rollers facing the guide ring are made such thatbetween the end faces of the rollers and the guide ring, there is onlypoint contact, preferably the distance between the roller axes and thepoint contacts of the end faces of the rollers with the guide ringamounting to roughly 50 to 75% of the maximum roller diameter. Themeasure of executing the ends face of the rollers facing the guide ringsuch that between the end faces of the rollers and the guide ring thereis only point contact can be accomplished in particular differently,specifically, either by the end faces of the rollers facing the guidering being convexly curved, or by the rollers on the end faces whichface the guide ring being provided with a bezel.

The above described measures ensure that with allowable crossing of therollers, no contact of the edges of the end faces of the rollers withthe guide rings occurs, so that “scoring” on the edges of the end facesof the rollers is precluded.

In particular, there are a host of possibilities for embodying theself-aligning roller bearing in accordance with the present invention

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic of one half of a self-aligning roller bearingin accordance with one embodiment of the present invention viewed in theaxial section,

FIG. 2 shows an enlarged extract of the transition between a roller andthe guide ring from the self-aligning roller bearing as shown in FIG. 1and

FIG. 3 shows in an overhead view a schematic representation of thecontact between the rollers and the guide ring in a self-aligning rollerbearing as shown in FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows one half of a self-aligning roller bearing 1 in an axialsection. The selfaligning roller bearing 1 includes of two rows ofsymmetrical rollers 2, 3 which are provided between an outer ring 4 witha curved outer track 5 and an inner ring 6 with two curved inner tracks7, 8. Between the two rollers 2 and 3 of the two rows of rollers (ofwhich the rollers 2, 3 are a part), there is a guide ring 9 which ismade as a circular ring disk and which has a rectangular cross section.The cross sectional center line 10 of the guide ring 9 runs parallel tothe bearing axis 11. Conversely the roller axes 12, 13 of the rollers 2and 3 run at an angle to the bearing axis 11. This angle is labelled thebearing pressure angle and in the self-aligning roller bearings,typically has a value between 4° and 18°.

In the embodiment shown, the guide ring 9 is dimensioned such that therollers 2, 3 are axially prestressed. Therefore, a force is exerted onthe rollers 2, 3 at an acute angle to the rouer axes 12, 13 by the guidering 9. In this way, displacement of the contact points between therollers 2, 3 and the outer track 5 and the inner tracks 6, 7 isaccomplished. Therefore, the pressure ellipses between the inner tracks6, 7 and the rollers 2, 3 are shifted to the end faces of theself-aligning roller bearing in accordance with the present invention.By displacement of the contact points or the pressure ellipses, thelines of force action of the outer ring 4 and outer track 5 - rollers 2,3 and rollers 2, 3 - inner ring 6 and inner tracks 7, 8 are at an angle,by which crossing of the rollers 2, 3 is reduced

In this embodiment furthermore, the guide ring 9 is made loose, i.e. itis guided on the inner ring 6, but it can move perpendicular to thebearing axis 11 in the direction to the outer ring 4. Because the guidering 9 is made loose, a material can easily be used which is differentthan for the inner ring 6. But mainly, the loose guide ring 9 has theadvantage that the peripheral component of the guide ring speed isbalanced by the concomitant turning of the guide ring 9, i.e. approacheszero.

A measure implemented in the embodiment is of quite special importance,specifically that the end faces 14 of the rollers 2, 3 facing the guidering 9 are made such that between the end faces 14 and the guide ring 9,there is only point contact. Preferably, the distance between the rolleraxes 12, 13 and the point contacts of the end faces 14 with the guidering 9 is roughly 50% to 75% of the maximum roller diameter.

The measure of making of the end faces 14 of the rollers 2, 3 facing theguide ring 9 such that between the end faces 14 and the guide ring 9,there is only point contact can be accomplished in various ways. Onepossibility is to make the end faces of the rollers 2, 3 facing theguide ring 9 convexly curved. Another possibility is accomplished in theembodiment shown; where the rollers 2, 3 are provided with a bezel 15 onthe end faces 14 which face the guide ring 9. Preferably, the transitionfrom the actual end faces 14 of the rollers 2, 3 is rounded or brokentowards the respective bezel 15; so that this transition is notsharp-edged.

The bezel angle 16, therefore the angle between the actual end faces 14of the rollers 2, 3 and the bezels 15 is preferably roughly 1.5° greaterthan the bearing pressure angle which is set in operation. As shown inFIG. 2, this results in that between the rollers 2, 3 and the guide ring9—more accurately between the end faces 14 of the rollers 2, 3 and theguide ring 9—there is always an opening angle 17 which arises from thedifference from the bezel angle 16 and the bearing pressure angle. It isensured by the opening angle 17 that between the end faces 14 of therollers 2, 3 and the guide ring 9 at rest, only one point of contactoccurs in operation, so that when relative movements occur in operation,only ever linear contact occurs. In addition the gap described by theopening angle 17 between the guide ring 9 and the rollers 2, 3 can beused to build up and maintain a lubricant film.

FIG. 3 shows the contact situation between the end faces 14 of therollers 2, 3 and the guide ring 9 in an overhead view. Also, when therollers 2, 3 cross by a crossing angle 18, contact of the edges 19 ofthe end faces 14 of the rollers 2, 3 with the guide ring 9 does notoccur, so that scoring on the edges 19 of the end faces 14 of therollers 2, 3 is precluded. This is shown in FIG. 3 by the position ofthe roller 3 which is shown by the broken line. Due to the crossing ofthe roller 3 by the crossing angle 18, the centerpoint of the end face14 of the roller 3 migrates by only a small amount out of its originallocation. However the running behavior of the self-aligning rollerbearing 1 is not noticeably influenced. In particular, there is nocontact of the edge 19 of the roller 3 with the guide ring 9. Thus theroller 3 is not destroyed, by which the service life of theself-aligning roller bearing 1 is increased overall.

Combined implementation of the following measures is of specialimportance for the self-aligning roller bearing 1 in accordance with theillustrated embodiment of the present invention.

a) guide ring 9 with a rectangular cross section.

b) dimensioning of the guide ring 9 such that the rollers 2, 3 areaxially prestressed

c) embodiment of the end faces 14 of the rollers 2, 3 facing the guidering 9 such that between the end faces 14 of the rollers 2, 3 and theguide ring 9, there is only point contact.

Tests have shown that in the joint implementation of the aforementionedmeasures, the friction which occurs in the self-aligning roller bearing1 in accordance with the present invention is roughly 30 to even 50%less than the friction which occurs in comparable known self-aligningroller bearings.

What is claimed is:
 1. A self-aligning roller bearing comprising: anouter ring with a curved outer track; an inner ring disposed within saidouter ring, said inner ring including two curved inner tracks; two rowsof rollers disposed between said outer ring and said inner ring, each ofsaid two rows of rollers including a plurality of rollers; and a guidering positioned between said two rows of rollers, said guide ring havinga rectangular cross section and a cross sectional center line whichextends parallel to an axial bearing axis.
 2. The self-aligning rollerbearing of claim 1, wherein said guide ring is a circular ring disk. 3.The self-aligning roller bearing of claim 1, wherein said guide ring isrotatable around said inner ring.
 4. The self-aligning roller bearing ofclaim 1, wherein said guide ring is dimensioned in a manner to causeaxial prestress of said two rows of rollers.
 5. The self-aligning rollerbearing of claim 1, wherein end faces of said plurality of rollers whichface said guide ring are adapted to make a point contact with said guidering.
 6. The self-aligning roller bearing of claim 5, wherein said pointcontact between said end faces and said guide ring is at a distance in arange of about 50% to 75% of a maximum roller diameter from a rolleraxis.
 7. The self-aligning roller bearing of claim 5, wherein said pointcontact between said end faces and said guide ring is positioned from aroller axis at a distance in a range of about 50% to 75% of a distancebetween at least one of said two inner tracks and a roller axis.
 8. Theself-aligning roller bearing of claim 5, wherein said end faces of saidplurality of rollers which face said guide ring are convexly curved. 9.The self-aligning roller bearing of claim 5, wherein said end faces ofsaid plurality of rollers which face said guide ring include a bezel.10. The self-aligning roller bearing of claim 9, wherein an angle ofsaid bezel is different than a bearing pressure angle.
 11. Theself-aligning roller bearing of claim 10, wherein said angle of saidbezel is between 0.3° to 5° greater than said bearing pressure angleduring operation of said self-aligning roller bearing.
 12. Theself-aligning roller bearing of claim 11, wherein said angle of saidbezel is approximately 1.5° greater than said bearing pressure angle.